Have you reviewed this troubleshooting guide from the manufacture? A one-off boiler service (recommended annually) can be carried out for a standard charge of just £ (including vat). We are the domestic heating contractor of the year. Service was great and i would highly recommend koegel to anyone if you need plumbing done they're the ones to call! You must also pass the industry approved bpec aptitude & selection test, which will be carried out.